Stretch fabrics of polyestercotton blends



United States Patent 3,507,609 STRETCH FABRICS 0F POLYESTER- COTTON BLENDS Adly Abdel-Moniem Gorrafa, Wilmington, Del., assignor to E. I. du Pout de Nemours and Company, Wilmington, DeL, a corporation of Delaware N0 Drawing. Filed Apr. 21, 1965, Ser. No. 449,861 Int. Cl. D06m 1/06, 9/04 US. Cl. 8-115.7 6 Claims ABSTRACT OF THE DISCLOSURE The improvement for imparting to a fabric of polyester and cotton fibers, in at least one fabric direction, a high degree of recoverable stretch with a low degree of growth, which comprises forming the yarn of a polyester cotton blend containing high shrinkage polyester fibers and cotton fibers, treating the fabric without tension with a mixture of methylene chloride and strong aqueous sodium hydroxide solution to shrink the fabric at least 10% and then washing the fabric.

This invention relates to a process for producing a highly stretchable woven or knitted fabric, and is more particularly concerned with a process for producing a high-bulk, highly stretchable, low-growth fabric from yarn composed of a blend of polyester and cellulosic fiber material.

Stretch fabrics containing no rubber or other elastomeric fibrous material have recently become highly desirable in the trade. Accordingly, increased efforts have been made to find a method for imparting a high degree of stretch in a fabric knitted or woven from yarn composed of a blend of polyester staple and cotton. Stretch fabrics of these components would be highly desirable in order to take advantage of the known special properties of polyester/cellulosic blends, such as washand-wear qualities, wrinkle resistance, strength and good textile aesthetics.

Previous attempts to make cotton or blendedyarn stretch fabrics by the chemical methods of the prior art have been unsatisfactory. For example, cotton fabrics treated by the process of slack-mercerization which pro vides only a low degree of stretch for a given fabric construction, also do not recover well from the stretched condition, and thus have a tendency to grow. In order to improve the recovery property of cotton or cottoncontaining fabrics, it is usually necessary to use a thermosetting resin in order to fix the shrunk fabric so that it has a better tendency to retract from stretching. However, this resin treatment usually causes a serious degradation of fabric strength. In the case of blended-yarn fabrics, a stepwise shrinkage method of imparting stretch, in which first one of the fiber components of the yarn is treated and allowed to shrink and then the other fiber component is treated and allowed to shrink, has been found unsatisfactory. The resulting fabrics possess a relatively low tendency to stretch.

It is an object of this invention to provide a process for producing a stretch fabric, of yarn composed of a blend of cotton and polyester fibers, which possesses the desirable features of polyester-and-cotton blend fabrics together with a potential to stretch from about 14% to 25 of its unstretched dimensions. It is a further object of this invention to provide a stretch fabric, composed of this same blended yarn, which has a high degree of dimensional recovery from its stretched state. Other objects will become apparent from the specification and claims.

In accordance with this invention a surprising improvement, in the process of producing fabric from yarn composed of a. blend of polyester fibers and cotton, is obtained when fabric formed of yarn containing at least 30% high-shrinkage polyester fiber and at least 20% cotton fiber is treated, in the absence of tension on the high-shrinkage yarn, with a mixture of methylene chloride and strong aqueous sodium hydroxide solution to shrink the polyester and cotton fibers simultaneously to provide a fabric shrinkage of at least 10%. The fabric is then removed from the mixture and washed with water until free of the shrinkage agents. The simultaneous shrinkage process is then followed by the finishing operations well known in the art for treating polyester/ cotton blend fabrics, preferably including a heat-setting step. By this process fabric can be prepared which has a widthwise stretch of at least 14% and a widthwise growth of less than 6.3% after being held extended at of the stretch potential for 2 hours and then allowed 1 hour to recover.

In the practice of this invention, the mixture of sodium hydroxide and methylene chloride can be stirred continuously to insure uniform impregnation of the polyester and cotton fibers. However, a suitable emulsifying agent is preferably used to eliminate the necessity for continuous stirring.

When stretch is to be imparted in only one fabric direction, the yarn containing high shrinkage polyester fibers is preferably used in the fill direction. A preferred sequence of fabric treatment consists of cold washing, ex-

traction to about 20% moisture, padding with a mixture or emulsion consisting of about equal volumes of methylene chloride and an aqueous sodium hydroxide solution containing about 25% sodium hydroxide, and then a final cold wash. Scouring, bleaching, dyeing, etc., can follow according to normal finishing of polyester/cotton blend fabric, but under minimum widthwise tension.

When stretch is to be imparted to a Woven fabric in the warp direction as well as in the fill direction, yarn containing high shrinkage polyester fibers is used in both directions. The preferred sequence of treatment to produce stretch in both the warp and fill directions of a fabric is to cold wash, extract to about 20% moisture, pad the fabric with the said caustic/methylene chloride .mixture, immerse it into the said mixture for further impregnation, and then remove the agents by a final cold wash. Bleaching, and other finishing steps are performed under minimum tension.

In the process of producing the yarn to be treated in accordance with this invention, the conventional cotton spinning system is preferably used. In this process, cotton and polyester staple are either picker-blended, or slivers of cotton and slivers of polyester are draw-frame blended. Drafted slivers are then reduced in size and twisted in conventional fashion to produce the yarn. A part or all of the polyester content of the yarn can be one or more continuous filaments, suitably incorporated in the yarn, e.g., core spun or plied. The term fiber, as

used herein, is intended to include both continuous filaments and staple fibers.

To produce acceptable stretch fabrics in accordance With this invention, at least 30% of the fiber must be high shrinkage fibers, which may be continuous filaments and/ or cut from high-shrinkage polyester filaments. A normal-shrinkage polyester fiber is one which shrinks less than 8% of its initial length upon immersion in boiling water, and a high-shrinkage polyester fiber is one which shrinks more than 10% (preferably from 15 to 60%) of its length upon immersion into boiling water. Processes for producing high-shrinkage polyester (polyethylene terephthalate) filaments are well known in the art. For example, the jet quenching procedure described in Kilian US. Patent No. 3,050,821 dated Aug. 28, 1962, combined with the drawing procedure described in Calton US. Patent No. 2,734,794 dated Feb. 14, 1956, (absent hotrelaxation) produces a very high-shrinkage polyester filament. It is also known that if a polyester is warm-wetdrawn according to procedures of Paulsen US. Patent No. 2,918,346, dated Dec. 22, 1959, and dried to a temperature below 90 C., the yarn remains highly amorphous and has a high degree of shrinkage when immersed in boiling water. In general, any high-shrinkage polyester fiber, regardless of how the ability to shrink is imparted to the fiber, will produce an acceptable fabric in accordance with this invention.

This invention is further illustrated by the following examples of preferred embodiments, although it will be understood that these examples are included for the purpose of illustration, and are not intended to limit the scope of the invention.

EXAMPLE I Two grey woven fabrics (A and B below) are prepared according to the following specifications: For the warp, a blend of 65% of normal-shrinkage polyethylene terephthalate staple and 35% cotton is spun to 50/1 cc. (11.8 tex) yarn with a twist of 25.5 turns/inch (10 turns/ cm.). For the filling, a blend of 33% high-shrinkage polyethylene terephthalate staple, 33% normal-shrinkage polyethylene terephthalate staple, and 34% cotton is used. This blend is spun to 50/1 cc. (11.8 tex) yarn, with 21.5 turns/inch (8.5 turns/cm.), for fabric A. The same blend is spun to 30/1 cc. (19.7 tex) yarn, with a twist of 16.5 turns/inch (6.5 turns/cm.), for fabric B. The loom construction of both fabrics is 60 ends/inch (23.6 ends/cm.) X 72 picks/inch (28.3 picks/cm.).

Each fabric is then cut into 2 swatches. The first swatch is dipped into a 25% aqueous solution of NaOH (slackmercerization process) for 5 minutes. The second swatch is dipped into a mixture consisting of equal volumes of 25% aqueous NaOH and methylene chloride to which has been added 1% by volume of a saturated hydrocarbon sodium sulfonate which acts as an emulsifying agent, for 5 minutes under substantially no widthwise tension. All swatches are then cold-washed, rinsed, scoured, bleached, and dried. The widthwise shrinkage results are as follows:

Pre-treatment: Shrinkage percent Fabric A- Slack-mercerization 12.7 NaOH/CH Cl 18.7 Fabric B Slack-mercerization 10.5 NaOH/CH cl 17.6

The higher degree of shrinkage brought about by the simultaneous shrinkage process is clearly shown.

EXAMPLE II This example illustrates the high degree of recoverable stretch with low growth provided by the present invention, and the improvement obtained in comparison with prior art slack mercerization treatment, for various fabrics. The results are summarized in the table.

Plain woven fabrics, designated by number in the table, are prepared according to the following specifications:

(1) For the warp, a blend of 65 normal-shrinkage polyethylene terephthalate staple and 35% cotton is spun to 50/1 cc. (11.8 tex) yarn with a twist of 25.5 turns/ inch (10 turns/ centimeter). For the filling, the same yarn is used. The loom construction of this fabric is ends/ inch (23.6 ends/cm.) x 72 picks/inch (28.3 picks/cm.).

(2) The same as Fabric 1 in all respects except that the filling yarn is 30/1 cc. (19.7 tex) spun with a twist of 18.1 turns/inch (7.1 turns/cm.).

(3) The same as Fabric 1 except that the filling'yarn is a blend of high-shrinkage polyethylene terephthalate staple and 35% cotton spun to 50/1 cc. (11.8 tex) with a twist of 25 .5 turns/ inch (10 turns/cm.). The high-shrinkage staple is cut from continuous filaments which shrink about 60% of the initial length upon immersion in boiling water.

(4) Similar to Fabric 3 but with high-shrinkage polyester/ cotton yarn used for both warp and filling; the loom construction of the fabric is the same as that of Fabric 1. The warp yarn is spun with a twist of 24.7 S turns/ inch (9.7 turns/cm.) and the filling yarn is spun with 24.7 Z turns/inch, both being otherwise identical to the filling yarn of Fabric 3.

(5) The same as Fabric 1 except that they filling yarn is prepared by core-spinning 60 denier continuous filament, high-shrinkage polyethylene terephthalate yarn with a blend of 65 normal-shrinkage polyethylene terephthalate staple and 35% cotton to 30/1 cc. (19.7 tex) yarn having a twist of 25.5 turns/inch (10 turns/ cm.). This core-spun yarn contains about 34% of high shrinkage filaments which shrink about 32% upon immersion in boiling water.

The above fabrics are cold-washed and extracted to about 20% moisture. They are then processed as indicated in the table by treatments described below. The conven tional finishing procedure referred to below consists of padding the fabric with an enzyme for desizing, crabbing, beck scouring, beck bleaching, drying, decating, heatsetting, singeing, light scouring, drying, and semi-decating; it will be understood that variations in these finishing steps will not have a significant effect on the results shown in the table.

In the fabric treatment designated NaOH/CH Cl in the table, the fabric is immersed at room temperature for 15 minutes 10 minutes for Fabric 4) in a mixture of equal volumes of 25% aqueous sodium hydroxide and methylene chloride, emulsified with 1% by volume of a saturated hydrocarbon sodium sulfonate emulsifying agent. This treatment is performed while the fabric is under substantially no widthwise tension (lengthwise tension is also avoided for Fabric 4, which has high shrinkage polyester fiber in both yarn directions). The fabric is then cold-washed, rinsed, and finished according to conventional polyester/cotton finishing procedure, but avoiding tension in the fabric stretch direction or directions.

In the fabric treatment designated slack mercerization in the table, the fabric is immersed at room temperature for 15 minutes in a 25 aqueous sodium hydroxide solution in accordance with the well-known slack mercerization process. The fabric is then cold-washed, rinsed and finished according to conventional polyester/cotton finishing procedure, with the exception that widthwise tension is avoided.

In the fabric treatment designated none in the table,

the above treatments with NaOH/CH Cl or 25 aqueous sodium hydroxide solution are omitted, but the fabric is finished according to conventional polyester/ cotton finishing procedure.

TABLE Widthwise Warpwise Widthwise growth (percent UTS) Finished stretch, stretch, construc- Weight Fabric Fabric treatment percent percent 0.5 min. 1.0 min. 5 min. 60 min. tion oz. lydfi Slack mercerization 3. 2 2. 9 2. 6 2. 1 74 x 80 2. 35 do 2. 2 2.1 1. 7 1. 6 74 x 79 3. 20 9. 1 8. 7 7. 6 6. 3 89 x 87 3. 26 8.0 7.7 6.7 4.5 90x96 3.71 (a) NBOH/CHzClz 2. 9 2. 7 2. 2 1. 7 88 x 87 4. 37 5 (b) Slack mercerizatlon 1. 2 1.1 9 0.8 82 x 78 3. 68 (c) None 1. 1. 1.4 1.2 861 79 3. 78

1 UTS percent measured after the fabric has been held for 2 hours at 85% of its stretch potential and allowed to recover for the indicated time The table gives the finished construction in finished warp ends per inch x finished picks per inch. The stretch is measured according to the formula:

Percent stretch X 100 where L=measured fabric length after releasing tension and allowing a specific relaxation period; L =original unstretched fabric length, e.g., 50 cm. The table gives values of UTS percent measured after the fabric is stretched to 85% of its stretch potential and so held for two hours, then released. The column heading indicates the time allowed after the tension is released from the fabric before the length measurement L is made.

The values of UTS percent measured according to the test procedure described above are obviously affected by the elongation at which the fabric is held under tension for two hours before it is relaxed and measured. Thus each of the UTS percent values obtained for Fabric 4 is reduced when stretched to only 61.5% of its stretch potential, instead of 85% of its stretch potential, to less than one-half of the value given in the table for the same recovery time.

It can readily be seen from the results given in the table for Fabrics 3, 4 and 5 that fabrics prepared in accordance with this invention possess a very high degree of stretch and a low degree of growth for a given amount of stretch, as exemplified by high percentage stretch and low Unrecovered Tensile Strain, respectively.

The concentration of sodium hydroxide to be used in the practice of this invention is preferably about 25% by weight; however, any concentration from 20-30% by weight is entirely satisfactory. The volumetric ratio of sodium hydroxide solution to methylene chloride solution is preferably about 1:1, although, depending on the ratio of cotton to high-shrinkage polyester content, reasonable variations in this ratio are suitable.

Percent UTS= X 100 Many variations may be employed in accordance with this invention without departing from the spirit and scope of this specification. For example, the yarn can contain cellulosic fibers other than cotton and the amount of cellulosic fiber in proportion to the amount of polyester fiber in the yarn can be varied within reasonable limits to pro duce stretch fabrics in accordance with this invention. The yarn twist may be varied within reasonable limits to vary the amount of shrinkage. Thus, when a twist multiplier of 3.0 is used instead of a twist multiplier of 4.0, shrinkage is enhanced and consequently the fabric has a higher degree of stretch. In regard to the immersion in, or padding of the fabrics with the sodium hydroxide/methylene chloride mixture, only a few seconds contact is required. A IO-seconds immersion in a mixture containing an equal volume of 20% aqueous sodium hydroxide and methylene chloride induces about the same degree of shrinkage as 30 seconds immersion in the same mixture.

This invention is applicable to both woven and knitted fabrics. For example, it can be applied to plain weaves, twill weaves, basket weaves, satin weaves, or sateen weaves. Many mixed yarns may be used in accordance with this invention. Two, three, or more types of polyester fiber materials possessing different shrinkage characteristics can be mixed with cotton or other cellulosic fiber in the blended yarn to be woven into a fabric to produce a stretch quality in the fabric. In addition to the polyester and cellulosic components, fibers such as acrylic, polyamide, modacrylic and others can be included in the blend. However, it is necessary that one of these be a high-shrinkage polyethylene terephthalate fiber and another be cellulosic fiber. This invention is also applicable to yarns and fabrics made of two or more blended fibers adequately shrunk simultaneously by two or more suitable chemical agents. This invention is further applicable to fabrics made from yarns having one component which is in a continuous filament form.

The products of this invention may be used to produce all types of stretch wearing apparel and home furnishings, for example, shirts, slip covers for furniture, and bed sheets. It has also been shown that the products of this invention are easily molded into shaped forms as, for instance, brassiere cups.

The important advantages of the products obtained by the process of this invention are that they possess a high degree of stretch and a low degree of Unrecovered Tensile Strain. These fabrics also have the advantage of possessing greater bulk than the conventional polyester/ cotton fabrics. A further advantage lies in the fact that a high ratio of polyethylene terephthalate staple to cotton may be used to make the yarn for the fabric because the polyester staple does not act to bind the shrinkage of cotton as in the prior art, but is used to complement the shrinkage, and therefore increases the propensity of the cotton to stretch. This feature enhances the desirable properties of the products of this invention because a high percentage of polyethylene terephthalate staple insures good Wash-and-wear properties of the fabrics produced from this yarn.

Similarly, in a reverse manner, the simultaneous shrinkage of cotton by the treatment complements rather than binds the shrinkage of the polyester, thus resulting in a higher total fabric shrinkage and consequently a higher fabric stretch.

Since many different embodiments of the invention may be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited by the specific illustrations except to the extent defined in the following claims.

Iclaim:

1. In the process of producing fabric from yarn comprising a blend of polyethylene terephthalate fibers and cotton, which includes the steps of forming the yarn, and then weaving or knitting the yarn to form the fabric; the improvement for imparting to the fabric, in at least one fabric direction, a high degree of recoverable stretch with a low degree of growth, which comprises forming the yarn used in said fabric direction of a polyester/cotton blend containing at least 30% of high-shrinkage polyesterfibers and-at least 20%" of cotton fibers; treatthe fabric in water; said mixture containing a sufficient.

concentration of methylene chloride to effectively shrink said polyethylene terephthalate fibers and a sufficient concentration of sodium hydroxide to effectively shrink said cotton.

2. A process as defined in claim 1 wherein the highshrinkage polyester fibers used in said polyester/cotton blend shrink about to 60% upon immersion in boiling water.

3. A process as defined in claim 1 wherein said blend of high shrinkage polyester/cotton blend contains less than 50% of normal polyester fibers which shrink less than 8% upon immersion in boiling water.

4. A process as defined in claim 1 wherein said highshrinkage polyester fibers are continuous filaments.

5. A process as defined in claim 1 wherein the fabric is shrunk in a mixture of about equal volumes of methylene chloride and an aqueous solution containing to by weight of sodium hydroxide.

6. A fabric produced by the process defined in claim 1 which has a widthwise stretch of at least 14 percent and a-Widthwise growth of-less than percent; after-being held for 2 hours at percent of the stretch potential and then allowed one hour to recover.'- j

References Cited v U UNITED STATES. PATENTS" 2,159,016 5/1939 Dreyfus a s 11s.7 X 2,974,002 3/1961 Hedrick s .1 2s 3,124,860 3/1964 Kenyon et al. ]8125 X 3,239,586 3/1966 Adams 8115.7'X 3,290,752 12/1966 Orrnand 8130.1 X

OTHER REFERENCES Sloan et al., Stretchable Cotton FabricsProperties and. Processing Techniques, article in American Dyestuif Re: porter, May 27, 1963, pp. 26 to 33.

HERBERT B. GUYN-N, Primary Examiner U.S.- c1. XQR. 

